A universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from a global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access (W-CDMA) technologies.
In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the United States, and TTA of Korea formed a Third Generation Partnership Project (3GPP) for creating detailed specifications of the UMTS technology. Within the 3GPP, in order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created for determining the specification of the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the specifications for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
A related art UMTS network structure 1 is illustrated in FIG. 1. As shown, a mobile terminal, or user equipment (UE) 2 is connected to a core network (CN) 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains and manages a radio access bearer for communications between the UE 2 and the core network 4 to meet end-to-end quality of service requirements.
The UTRAN 6 includes a plurality of radio network subsystems (RNS) 8, each of which comprises one radio network controller (RNC) 10 for a plurality base stations, or Node Bs 12. The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. One or more cells exist in one Node B. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit a downlink signals to the UE 2. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer to the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and the UTRAN 6 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example, 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is well known in communications systems.
A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into a physical layer, a data link layer, and a network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. The transport channel is divided into a dedicated transport channel and a common transport channel depending on whether a channel is shared. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (receiver).
The second layer includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer and a packet data convergence protocol (PDCP) layer. The MAC layer maps various logical channels to various transport channels. The MAC layer also multiplexes logical channels by mapping several logical channels to one transport channel. The MAC layer is connected to an upper RLC layer via the logical channel. The logical channel can be divided into a control channel for transmitting control plane information a traffic channel for transmitting user plane information according to the type of information transmitted.
The MAC layer is divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs sublayer and a MAC-e sublayer according to the type of transport channel being managed. The MAC-b sublayer manages a broadcast channel (BCH), which is a transport channel handling the broadcast of system information. The MAC-c/sh sublayer manages common transport channels such as an FACH (Forward Access Channel) or a DSCH (Downlink Shared Channel) that is shared by other terminals. The MAC-d sublayer handles the managing of a DCH (Dedicated Channel), namely, a dedicated transport channel for a specific terminal. In order to support uplink and downlink high speed data transmissions, the MAC-hs sublayer manages an HS-DSCH (High Speed Downlink Shared Channel), namely, a transport channel for high speed downlink data transmission, and the MAC-e sublayer manages an E-DCH (Enhanced Dedicated Channel), namely, a transport channel for high speed uplink data transmissions.
The RLC layer guarantees a quality of service (QoS) of each radio bearer (RB) and handles the transmission of corresponding data. The RLC layer includes one or two independent RLC entities for each RB in order to guarantee a particular QoS of each RB. The RLC layer also provides three RLC modes, namely, a Transparent Mode (TM, an Unacknowledged Mode (UM) and an Acknowledged Mode (AM), to support various types of QoS. Also, the RLC controls the size of data to be suitable for a lower layer in transmitting over a radio interface. For this purpose, the RLC segments and concatenates the data received from the upper layer.
A PDCP (Packet Data Convergence Protocol) layer is a higher layer of the RLC layer and allows the data transmitted through a network protocol (such as an IPv4 or IPv6) to be effectively transmitted over a radio interface with a relatively small bandwidth. To achieve this, the PDCP layer performs a header compression function wherein only necessary information is transmitted in a header part of the data to thereby increase transmission efficiency over the radio interface. Because the PDCP layer performs the header compression as a basic function, it exists only at a packet switched (PS) domain. One PDCP entity is provided per RB to provide an effective header compression function with respect to each PS service.
A BMC (Broadcast/Multicast Control) layer, located at an upper portion of the RLC layer in the second layer (L2), schedules a cell broadcast message and broadcasts the message to terminals located in a specific cell.
A radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is defined in the control plane and controls the parameters of the first and second layers with respect to the establishment, reconfiguration and release of RBs. The RRC layer also controls logical channels, transport channels and physical channels. Here, the RB refers to a logical path provided by the first and second layers of the radio protocol for data transmission between the terminal and the UTRAN. In general, the establishment of the RB refers to stipulating the characteristics of a protocol layer and a channel required for providing a specific data service, and setting their respective detailed parameters and operation methods.
An HSUPA (High Speed Uplink Packet Access) will now be described in detail. The HSUPA is a system allowing a terminal or UE to transmit data to the UTRAN via the uplink at a high speed. The HSUPA employs an enhanced dedicated channel (E-DCH), instead of the related art dedicated channel (DCH), and also uses an HARQ (Hybrid ARQ) and AMC (Adaptive Modulation and Coding), required for high-speed transmissions, and a technique such as a Node B-controlled scheduling.
For the HSUPA, the Node B transmits to the terminal downlink control information for controlling the E-DCH transmission of the terminal. The downlink control information includes response information (ACK/NACK) for the HARQ, channel quality information for the AMC, E-DCH transmission rate allocation information for the Node B-controlled scheduling, E-DCH transmission start time and transmission time interval allocation information, transport block size information, and the like.
The terminal transmits uplink control information to the Node B. The uplink control information includes E-DCH transmission rate request information for Node B-controlled scheduling, UE buffer status information, UE power status information, and the like. The uplink and downlink control information for the HSUPA is transmitted via a physical control channel such as an E-DPCCH (Enhanced Dedicated Physical Control Channel).
For the HSUPA, a MAC-d flow is defined between the MAC-d and MAC-e. Here, a dedicated logical channel such as a DCCH (Dedicated Control Channel) or a DTCH (Dedicated Traffic Channel) is mapped to the MAC-d flow. The MAC-d flow is mapped to the transport channel E-DCH and the transport channel E-DCH is mapped to the physical channel E-DPDCH (Enhanced Dedicated Physical Data Channel). The dedicated logical channel can also be directly mapped to the transport channel DCH. In this case, the DCH is mapped to the physical channel DPDCH (Dedicated Physical Data Channel). Such inter-channel mapping relationships are shown in FIG. 3.
The MAC-d sublayer will now be described in detail. A transmitting side MAC-d sublayer forms a MAC-d PDU (Protocol Data Unit) from a MAC-d SDU received from the upper layer, such as the RLC layer. A receiving side MAC-d sublayer restores the MAC-d SDU from the MAC-d PDU received from the lower layer and delivers it to the upper layer, such as the RLC layer. At this time, the MAC-d sublayer exchanges the MAC-d PDU with the MAC-e sublayer through the MAC-d flow or exchanges the MAC-d PDU with the physical layer via the DCH. The MAC-d sublayer performs a function, such as transport channel type switching for selectively switching a transport channel according to an amount of data, ciphering/deciphering for performing ciphering or deciphering on the MAC-d PDU, TFC selection for selecting a transport format combination (TFC) suitable for a channel situation, and a C/T Mux for managing a logical channel identifier (C/T) for identifying each dedicated logical channel when several dedicated logical channels are multiplexed and are to be mapped to one DCH or to one MAC-d flow. A C/T field, such as a logical channel identifier, is used only when a logical channel is multiplexed, and added to a header of each MAC-d SDU to form the MAC-d PDU. Presently, the C/T field is defined to have 4 bits. Thus, the maximum number of logical channels that can be multiplexed to one DCH or one MAC-d flow is 16. The structure of the terminal, namely, the transmitting side of the MAC-d sublayer for the HSUPA, is shown in FIG. 4. A MAC-d format when the logical channels are multiplexed is shown in FIG. 5.
The transmitting side MAC-e sublayer forms the MAC-e PDU from the MAC-d PDU (namely, the MAC-e SDU), which is received through the MAC-d flow from the MAC-d sublayer. A receiving side MAC-e sublayer restores the MAC-e SDU from the MAC-e PDU received from the lower layer, namely, the physical layer and delivers it to the upper layer. In this case, the MAC-e sublayer exchanges the MAC-e PDU with the physical layer via the transport channel E-DCH.
The MAC-e sublayer performs a different function depending on whether it belongs to the transmitting side or to the receiving side. First, the transmitting side MAC-e sublayer performs a function of scheduling/priority handling. Preferably, it schedules a data transmission according to uplink/downlink control information and processes the data according to a priority level of the data. The transmitting side MAC-e also performs a function of hybrid ARQ, such as reliably transmitting data at a high speed, and a function of TFRC (Transport Format and Resource Combination) selection, such as transporting a format suitable for a channel situation and resource combination selection.
In particular, the scheduling/priority handling block also serves to form the MAC-e PDU to be transmitted to the physical channel. Specifically, the scheduling/priority handling block concatenates MAC-d PDUs (namely, MAC-e SDUs) received during a certain transmission time interval (TTI) through one MAC-d flow from the MAC-d sublayer according to their lengths. The scheduling/priority block then adds the length information to the MAC-e header, adds a 6-bit transmission sequence number (TSN) of the transport block to be transmitted to the header, and adds a 3-bit PID (Priority ID) for identifying a priority level of the MAC-d flow and a logical channel to the header. Finally, the scheduling/priority handling block adds a 1-bit version flag (VF) to the header to form the MAC-e PDU in order to later support a different MAC-e PDU format.
The structure of the transmitting side MAC-e sublayer and the MAC-e PDU format are shown in FIGS. 6 and 7. In general, a certain type of PDU format is used so that the receiving side receives data as a series of bit streams (e.g., 0, 1, 0, 1). Without determining a format, the receiving side cannot interpret each bit for what it means. In the HSUPA, the MAC-e PDU format is used with some restrictions, as shown in FIG. 7. The restrictions are explained below.
First, one MAC-e PDU is transmitted during one TTI. Thus, a TSN is added to every MAC-e PDU. Second, one MAC-e PDU includes only the data of logical channels which belong to the same MAC-d flow and has the same priority level. Thus, the PID is interpreted as a MAC-d flow ID+logical channel priority.
Third, the data of several logical channels are multiplexed to one MAC-e PDU in order to obtain multiplexing gain. In general, the length of the SDU can be different for each logical channel, so information indicating the length of each SDU is added to the header.
Of the above conditions, the length of the header of the MAC-e PDU is varied due to the third condition. The length information of the SDU includes three fields: a 3-bit SID (Size Index) field for indicating a length of each SDU, a 7-bit N field for indicating the number of SDUs having the length of the SID, and a 1-bit F (Flag) field for indicating whether the next field is the SID length information or a MAC-e SDU. Preferably, the length information of the SDU includes the three fields of SID, N and F, and its size (length) increases to correspond with the number of length types of the SDU.
In order to wirelessly transmit a certain PDU via the physical channel, the PDU must have a determined length required for coding, modulation and spreading performed in the physical channel. Thus, the MAC-e sublayer generates a PDU suitable for a size required by the physical channel by padding an end portion of the PDU. Such padding portion serves to fit the size of the PDU and does not contain any information. When the receiving side receives the PDU, it discards the padding portion.
The receiving side interprets the received bit streams according to the format shown in FIG. 7. Preferably, the receiving side interprets the bit streams starting from the VF (1 bit), PID (3 bits), TSN (6 bits), SID (3 bits), N (7 bits), F (1 bit), and interprets the header until the F field indicates that the next portion is the SDU. When the F field indicates that the next portion is the SDU, the receiving side, starting from the next bits, disassembles the SDU according to the length information of the SDU. Preferably, the SDU is disassembled according to the length and the number of SDUs from the combination of SID, N and F. After extracting the SDU, a remaining portion is discarded as a padding portion.
Notably, if the MAC-e SDU has the same length, the length information of one SDU can be used to inform the lengths of other SDUs despite the use of several logical channels for transmitting data. With reference to FIG. 7, the first SDU length information, specifically, the combination of SID1, N1 and F1, informs the data length of both a first logical channel (C/T=1) and a second logical channel (C/T=2), and Kth SDU length information, namely, the combination of SIDK, NK and FK informs the data length from the fourth logical channel (C/T=4) to the kth logical channel (C/T=k). Preferably, the MAC-e sublayer does not process the data by logical channel, but processes the data by the size of the MAC-e SDU.
The structure of the receiving side MAC-e sublayer is shown in FIG. 8. The HARQ block of the receiving side corresponds to the HARQ block of the transmitting side, and each HARQ process of the HARQ block performs an SAW (Stop And Wait) ARQ function with the transmitting side. When the receiving side receives one MAC-e PDU through the HARQ process, it reads the VF of the header of the MAC-e PDU to check its version, and checks the next PID field to recognize which MAC-d flow and which priority level the received PDU corresponds to. This operation is performed in a re-ordering queue distribution block. The PDU is then delivered to a reordering block indicated by the PID. The reordering function of the receiving side is notable compared with the transmitting side. That is, the MAC-e sublayer receives the MAC-e PDUs through the HARQ out-of-sequence, but the RLC layer (namely, the upper layer following the MAC-d sublayer) requests in-sequence delivery. Accordingly, the MAC-e sublayer performs reordering to sequentially deliver the non-sequentially received PDUs to the upper layer.
To perform the reordering, each PID has a reordering buffer. Although a certain PDU is successfully received, if the TSN is not in sequence, the PDU is temporarily stored in the buffer. Then, when an in-sequence delivery of the PDU is possible, it is delivered to the upper layer. A portion from the TSN, except for the VF and the PID of the header of the PDU, is stored in the reordering buffer. Thereafter, when the PDU is delivered to a disassembly block, the SDU is disassembled upon checking the SDU length information of the SID, N and F, and then delivered to the upper MAC-d sublayer. Preferably, only the MAC-e SDU (MAC-d PDU) is delivered through the MAC-d flow.
In the HSUPA, the structure of the MAC-d sublayer of the UTRAN (the receiving side) is similar to the MAC-d sublayer of the terminal (the transmitting side). Especially, portions of the receiving side related to the HSUPA perform the functions of the transmitting side, but in opposite order. As for the operations related to the DCH, the only difference is that the terminal performs the TFC selection, while the UTRAN performs the scheduling/priority handling. Referring to the HSUPA, regarding the MAC-d PDUs received through the MAC-d flow from the MAC-e sublayer, the C/T Mux block reads the C/T field to detect which logical channel the data (i.e., MAC-d PDUs) belongs to, removes the C/T field, extracts the MAC-d SDU and delivers it via a channel indicated by the C/T field to the upper RLC layer. As aforementioned, the C/T field does not always exist, but exists when logical channels are multiplexed. If logical channels are not multiplexed, the received MAC-d PDU is the MAC-d SDU, so the C/T Mux block delivers such to the RLC layer. FIG. 9 illustrates a structure of the MAC-d sub-layer of the UTRAN, the receiving side in the HSUPA.
In the related art, numerous overheads are added in constructing the MAC-d PDU. Especially, when logical channels are multiplexed, the 4-bit C/T field (namely, the logical channel identifier) is added to each MAC-e SDU. Thus, when numerous MAC-e SDUs are included in the MAC-e PDU, overheads of the MAC layer are considerably increased. Such increase in the overheads leads to the reduction of throughput, therefore failing to meet a desired transmission rate required for high speed data communication.